The present invention relates to an antibacterial coating for an implant and to a method of producing this coating.
It is generally known that silver has a high antibacterial activity. It is also already described in the prior art to use silver in a coating for implants. Examples are found in WO 2010/106164 A1 and in EP 1 632 198 B1. Such a coating offers advantages if the implant comes into contact with bacteria during the surgery or in the surgery wound, for example if bacteria reach the wound in an undesirable manner during the surgery or if bacteria are already present in the wound due to an existing infection.
But it is also known from the literature that silver ions also have a cytotoxic effect. This effect starts even with concentrations of above 380 μg/l (see, for example, Heidenau, F., Mittelmeier W., Detsch R., Haenle M., Stenzel F., Zeigler G., Gollwitzer H., 2005: “A novel antibacterial titania coating: Metal ion toxicity and in vitro surface colonization”, J. Materials Science, Materials in Medicine 16, 1-6″).
The cytotoxicity of silver ions that has been observed even with such low concentrations corresponds to the fact that silver does not play a role in the metabolism of the cell; silver is not part of the so-called essential trace elements in the human organism. The intake of low doses of silver, as well as a release from silver surfaces occurring over a longer period of time may lead to permanent cell damage. The WHO recommends that the consumption of silver should not exceed 180 μg per day (see, for example, Gibbins, B., Warner, L., 2005: “The Role of Antimicrobial Silver Nanotechnology”, MDDI, http://www.devicelink.com/mddi/archive/05/08/005.html, 05.02.08).
It is also known that copper has an antibacterial activity, which, however, is lower than the antibacterial activity of silver. In contrast to silver, copper ions, in moderate concentrations, do not cause cell damage (see the above-mentioned publication of Heidenau et al.); they are, however, of essential importance to the metabolism of the cells and are present in the body media at concentrations of from 11 to 24 μmol/l (see, for example, catalog of the Inst. f. Labordiagnostik Klinikum Süd, Rostock, Germany, 2005).
Accordingly, antibacterial coatings that use copper have also already been described in the prior art. One example is found in U.S. Pat. No. 5,958,440, in which an antibacterial coating with copper, among others, is applied by means of a PVD (physical vapor deposition) process. In that document, however, only layers having a limited hardness are obtained, which are not suitable for a number of applications.
The object of the invention is to propose surface layers which combine the existing advantages of the PVD layers, such as good adhesion and high hardness, with an antibacterial activity of the layer, and also a method for an effective production of such surface layers.